JP5664884B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that can reduce the amount of NOx (nitrogen oxide) emissions by effectively utilizing a three-way catalyst disposed in an exhaust passage.

  Conventionally, in order to purify exhaust gas discharged from an internal combustion engine, a three-way catalyst is disposed in the exhaust passage of the engine. As is well known, the three-way catalyst has an oxygen storage function. That is, when the gas flowing into the three-way catalyst (catalyst inflow gas) contains excess oxygen, the three-way catalyst stores the oxygen and purifies NOx. When the catalyst inflow gas contains excessive unburned substances, the three-way catalyst releases the stored oxygen and purifies the unburned substances. Hereinafter, the three-way catalyst is also simply referred to as “catalyst”.

  A conventional air-fuel ratio control device (conventional device) includes an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor that are disposed in the exhaust passage of the engine and upstream and downstream of the catalyst, respectively. In the conventional apparatus, the air / fuel ratio (detected upstream air / fuel ratio) represented by the output value of the upstream air / fuel ratio sensor is matched with the target air / fuel ratio (upstream target air / fuel ratio, target air / fuel ratio of catalyst inflow gas). The air-fuel ratio of the air-fuel mixture supplied to the engine (engine air-fuel ratio) is controlled. This control is also referred to as “main feedback control”.

  Further, the conventional apparatus calculates the sub feedback amount so that the output value of the downstream air fuel ratio sensor matches the “target value corresponding to the theoretical air fuel ratio”, and the upstream target air fuel ratio is substantially determined by the sub feedback amount. The air-fuel ratio of the engine is controlled by changing to (for example, refer to Patent Document 1). The air-fuel ratio control using the sub feedback amount is also referred to as “sub feedback control”.

JP 2009-162139 A

  By the way, when an acceleration operation is performed on the engine when the engine is “steadily operated with a certain amount of intake air”, in particular, the air-fuel ratio of the engine at the time of the acceleration operation (engine When the air-fuel ratio of the air-fuel mixture supplied to the engine is leaner than the stoichiometric air-fuel ratio, a large amount of NOx (nitrogen oxide) is discharged from the engine. In this case, if the NOx reduction rate of the catalyst (reaction rate for purifying NOx) is not sufficiently high, a large amount of NOx flowing into the catalyst is not sufficiently purified by the catalyst and flows out downstream of the catalyst. Such a situation occurs, for example, when a vehicle equipped with an engine is traveling at a relatively high speed and is accelerated for overtaking the preceding vehicle.

  The present invention has been made to address the above-described problems. That is, one of the objects of the present invention is that when a large amount of NOx is expected to flow into the catalyst, the state of the catalyst is changed in advance to a state in which the “NOx reduction rate” is high, thereby reducing the NOx. Another object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can reduce the amount of exhaust gas.

An internal combustion engine control apparatus (invention apparatus) according to the present invention comprises:
A catalyst disposed in an exhaust passage of the internal combustion engine;
A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
Air-fuel ratio control means for controlling the air-fuel ratio of the engine that is the air-fuel ratio of the air-fuel mixture supplied to the engine based on the output value of the downstream air-fuel ratio sensor;
Is provided.

Further, the air-fuel ratio control means includes:
Including a condition determination means for determining whether or not a predetermined condition (specific condition) for predicting that an operating state in which a large amount of nitrogen oxide flows into the catalyst has arrived,
When the predetermined condition is satisfied, at least one of the concentration of the reducing agent (unburned material) in the catalyst and the temperature of the catalyst is increased as compared with the case where the predetermined condition is not satisfied. The air / fuel ratio of the engine is controlled. Note that increasing the concentration of the reducing agent in the catalyst is synonymous with decreasing the oxygen storage amount of the catalyst.

The predetermined condition is, for example,
The intake air amount correlation value, which increases as the intake air amount of the engine increases, is larger than a low air amount threshold value and smaller than a high air amount threshold value greater than the low air amount threshold value; and This is a condition that is satisfied when at least one of the speed of the mounted vehicle is larger than the low-side speed threshold and smaller than the high-side speed threshold larger than the low-side speed threshold.
Further, it is desirable that the predetermined condition is a condition that is satisfied when the change amount per unit time of the intake air amount correlation value is smaller than a predetermined change amount threshold value.

  According to this, the concentration of the reducing agent in the catalyst is increased and / or the temperature of the catalyst is increased by the time when a large amount of nitrogen oxide flows into the catalyst. Therefore, when a large amount of nitrogen oxide flows into the catalyst, the NOx reduction rate of the catalyst is already high. Therefore, even when a large amount of NOx flows into the catalyst, most of the NOx can be purified (reduced) by the catalyst, so that the amount of NOx discharged can be reduced.

  In addition, it is not preferable to always maintain the concentration of the reducing agent in the catalyst at a high value because the possibility of unburned matter being discharged from the catalyst increases. However, in one aspect of the apparatus of the present invention, maintaining the concentration of the reducing agent in the catalyst at a high value is limited to the case where the predetermined condition is satisfied, and when the predetermined condition is satisfied, the engine Since the exhaust temperature of the catalyst is also high to some extent, the temperature of the catalyst is somewhat high. Therefore, the possibility of unburned material being discharged is small.

  Furthermore, it is not preferable to keep the temperature of the catalyst at a high temperature at all times because it causes deterioration of the catalyst (such as sintering). However, in one aspect of the apparatus of the present invention, the catalyst temperature is set to a high temperature only when the predetermined condition is satisfied, so that the deterioration of the catalyst does not proceed greatly.

In this case, the air-fuel ratio control means is
The average value of the air-fuel ratio of the engine when the predetermined condition is satisfied is smaller than the average value of the air-fuel ratio of the engine when the predetermined condition is not satisfied. By controlling the air-fuel ratio, the concentration of the reducing agent in the catalyst is increased when the predetermined condition is satisfied.

More specifically, in one aspect of the device of the present invention,
The air-fuel ratio control means includes target air-fuel ratio setting means and fuel supply amount control means.

  The target air-fuel ratio setting means tends to cause the oxygen storage amount of the catalyst to be excessive based on the output value of the downstream air-fuel ratio sensor, and to provide the catalyst with a rich air-fuel ratio gas smaller than the stoichiometric air-fuel ratio. When it is determined that a rich request for inflow has occurred, the target of the air-fuel ratio of the engine is set to a target rich air-fuel ratio that is smaller than the theoretical air-fuel ratio.

  Further, the target air-fuel ratio setting means has a lean air-fuel ratio gas larger than the stoichiometric air-fuel ratio in the catalyst, because the oxygen storage amount of the catalyst tends to be insufficient based on the output value of the downstream air-fuel ratio sensor. When it is determined that a lean request for inflowing has occurred, the target of the air / fuel ratio of the engine is set to a target lean air / fuel ratio that is larger than the stoichiometric air / fuel ratio.

  The fuel supply amount control means controls the amount of fuel supplied to the engine based on the set target air-fuel ratio.

In this case, the target air-fuel ratio setting means further includes
The target rich air-fuel ratio when the predetermined condition is satisfied is set to an air-fuel ratio smaller than the target rich air-fuel ratio when the predetermined condition is not satisfied.

Further, the target air-fuel ratio setting means includes:
When the change amount ΔVoxs per unit time of the output value of the downstream side air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | becomes larger than the lean determination threshold value dLeanth, the rich request is generated. And
When the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | is larger than the rich determination threshold value dRichth, it is determined that the lean request has occurred.

  According to this, the target rich air-fuel ratio when the predetermined condition is satisfied is smaller than the target rich air-fuel ratio when the predetermined condition is not satisfied. Therefore, when the predetermined condition is satisfied, the average value of the air-fuel ratio of the engine (therefore, the average value of the air-fuel ratio of the catalyst inflow gas that is the gas flowing into the catalyst) becomes small (becomes rich). The concentration of the reducing agent in the catalyst increases. Therefore, the state of the catalyst can be set to “a state in which the NOx reduction rate is increased”.

In another aspect of the apparatus of the present invention, the air-fuel ratio control means includes
When the change amount ΔVoxs per unit time of the output value of the downstream air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | becomes larger than the lean determination threshold dLeanth, the state of the catalyst is When it is determined that the oxygen excess state has occurred, and when the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | is greater than the rich determination threshold dRichth, the state of the catalyst is determined to be an oxygen-deficient state. Catalyst state determination means for determining that
When the catalyst state determining means determines that the state of the catalyst has changed from the oxygen-deficient state to the oxygen-excess state, when the lean delay time that is a predetermined delay time including 0 has elapsed, the engine From the time when the target of the air-fuel ratio is set to a target rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, and the catalyst state determining means determines that the state of the catalyst has changed from the oxygen excess state to the oxygen insufficient state Target air-fuel ratio setting means for setting a target air-fuel ratio of the engine to a target lean air-fuel ratio larger than the stoichiometric air-fuel ratio when a rich delay time that is a predetermined delay time including 0 has elapsed;
Fuel supply amount control means for controlling the amount of fuel supplied to the engine based on the set target air-fuel ratio;
Including
The target air-fuel ratio setting means further includes:
The rich delay time when the predetermined condition is satisfied is set to be longer than the rich delay time when the predetermined condition is not satisfied.

  According to this, when the predetermined condition is satisfied, the time during which the target air-fuel ratio is set to the rich air-fuel ratio is “rich delay time compared to when the predetermined condition is not satisfied. It becomes longer by “the longer time”. Therefore, the average value of the air-fuel ratio of the engine (and hence the average value of the air-fuel ratio of the catalyst inflow gas that is the gas flowing into the catalyst) becomes smaller (rich) than the stoichiometric air-fuel ratio. Therefore, when the predetermined condition is satisfied, the state of the catalyst can be set to “a state in which the NOx reduction rate is increased”.

Similarly, the air-fuel ratio control means includes
When the catalyst state determining means determines that the state of the catalyst has changed from the oxygen-deficient state to the oxygen-excess state, a lean delay time, which is a predetermined delay time, has elapsed. The target air-fuel ratio is set to a target rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and predetermined when the catalyst state determining means determines that the state of the catalyst has changed from the oxygen excess state to the oxygen insufficient state. Target air-fuel ratio setting means for setting the target air-fuel ratio of the engine to a target lean air-fuel ratio larger than the stoichiometric air-fuel ratio when a rich delay time including 0, which is the delay time of the engine, has elapsed,
Fuel supply amount control means for controlling the amount of fuel supplied to the engine based on the set target air-fuel ratio;
Including
The target air-fuel ratio setting means further includes:
The lean delay time when the predetermined condition is satisfied is set to be shorter than the lean delay time when the predetermined condition is not satisfied.

  According to this, when the predetermined condition is satisfied, the time during which the target air-fuel ratio is set to the rich air-fuel ratio is compared with the case where the predetermined condition is not satisfied. It becomes longer by “the shorter time”. Therefore, the average value of the air-fuel ratio of the engine (and hence the average value of the air-fuel ratio of the catalyst inflow gas that is the gas flowing into the catalyst) becomes smaller (rich) than the stoichiometric air-fuel ratio. Therefore, when the predetermined condition is satisfied, the state of the catalyst can be set to “a state in which the NOx reduction rate is increased”.

In another embodiment of the device of the present invention,
The air-fuel ratio control means includes
When the change amount ΔVoxs per unit time of the output value of the downstream side air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | becomes larger than the lean determination threshold value dLeanth, the air-fuel ratio of the engine Set the target air-fuel ratio to a target rich air-fuel ratio that is smaller than the theoretical air-fuel ratio,
When the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | is larger than the rich determination threshold dRichth, the target air-fuel ratio of the engine is made larger than the stoichiometric air-fuel ratio. Target air-fuel ratio setting means for setting the fuel ratio;
Fuel supply amount control means for controlling the amount of fuel supplied to the engine based on the set target air-fuel ratio;
including.

In this case, the target air-fuel ratio setting means is
The rich determination threshold value dRichth when the predetermined condition is satisfied is configured to be set to a value larger than the rich determination threshold value dRichth when the predetermined condition is not satisfied.

Alternatively, the target air-fuel ratio setting means includes
The lean determination threshold value dLeanth when the predetermined condition is satisfied is configured to be set to a value smaller than the lean determination threshold value dLeanth when the predetermined condition is not satisfied. The

  According to these, when the predetermined condition is satisfied, the period during which it is determined that the state of the catalyst is in an oxygen-deficient state is shorter than when the predetermined condition is not satisfied, The period during which the catalyst state is determined to be an oxygen-excess state is lengthened. Therefore, when the predetermined condition is satisfied, the time during which the target air-fuel ratio is set to the target rich air-fuel ratio becomes relatively long. Therefore, the average value of the air-fuel ratio of the engine (and hence the average value of the air-fuel ratio of the catalyst inflow gas that is the gas flowing into the catalyst) becomes smaller (rich) than the stoichiometric air-fuel ratio. Therefore, when the predetermined condition is satisfied, the state of the catalyst can be set to “a state in which the NOx reduction rate is increased”.

In another embodiment of the device of the present invention,
The air-fuel ratio control means includes
Based on the output value of the downstream air-fuel ratio sensor, it is determined that the oxygen storage amount of the catalyst tends to be excessive, and that a rich air-fuel ratio gas smaller than the stoichiometric air-fuel ratio should flow into the catalyst. When the target air-fuel ratio of the engine is set to a target rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, the oxygen storage amount of the catalyst tends to be insufficient, and the catalyst has a lean air-fuel ratio greater than the stoichiometric air-fuel ratio. A target air-fuel ratio setting means for setting a target lean air-fuel ratio larger than the stoichiometric air-fuel ratio when determining that the gas should be introduced;
Fuel supply amount control means for controlling the amount of fuel supplied to the engine based on the set target air-fuel ratio;
including.

In this case, the target air-fuel ratio setting means further includes
The target rich air-fuel ratio when the predetermined condition is satisfied is set to an air-fuel ratio smaller than the target rich air-fuel ratio when the predetermined condition is not satisfied, and the predetermined condition is satisfied By setting the target lean air-fuel ratio when the predetermined condition is not satisfied to an air-fuel ratio larger than the target lean air-fuel ratio when the predetermined condition is not satisfied, the amount of heat generated in the catalyst is increased. Increase the temperature of the catalyst. In this case, the average of the target rich air-fuel ratio when the predetermined condition is satisfied and the target lean air-fuel ratio when the predetermined condition is satisfied is greater than the theoretical air-fuel ratio or the theoretical air-fuel ratio. These target air-fuel ratios are preferably set so as to be small.

  According to this, when a predetermined condition is satisfied, the amplitude of the air-fuel ratio of the gas flowing into the catalyst increases. Accordingly, the reaction in the catalyst becomes active, so the reaction heat increases. As a result, when the predetermined condition is satisfied, the temperature of the catalyst can be increased as compared with the case where the predetermined condition is not satisfied. It is possible to set the status to “On”.

  Other objects, other features and attendant advantages of the apparatus of the present invention will be readily understood from the description of each embodiment of the present invention described with reference to the following drawings.

FIG. 1 is a schematic plan view of an internal combustion engine to which an air-fuel ratio control apparatus according to each embodiment of the present invention is applied. FIG. 2 is a graph showing the relationship between the air-fuel ratio (upstream air-fuel ratio) of the gas flowing into the catalyst shown in FIG. 1 and the output value of the upstream air-fuel ratio sensor shown in FIG. FIG. 3 is a graph showing the relationship between the air-fuel ratio (downstream air-fuel ratio) of the gas flowing out from the catalyst shown in FIG. 1 and the output value of the downstream air-fuel ratio sensor shown in FIG. FIG. 4 is a time chart showing the target air-fuel ratio changed by the control device (first control device) according to the first embodiment of the present invention. FIG. 5 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 6 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 7 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 8 is a flowchart showing a routine executed by the CPU of the first control device. FIG. 9 is a time chart showing a catalyst lean state display flag and a rich request flag used by the control device (second control device) according to the second embodiment of the present invention. FIG. 10 is a flowchart showing a routine executed by the CPU of the second control device. FIG. 11 is a flowchart showing a routine executed by the CPU of the second control device. FIG. 12 shows the output value of the downstream air-fuel ratio sensor shown in FIG. 1, the catalyst lean state display flag and the rich request flag used by the control device (third control device) according to the third embodiment of the present invention, It is the time chart which showed. FIG. 13 is a flowchart showing a routine executed by the CPU of the third control device. FIG. 14 is a flowchart showing a routine executed by the CPU of the control device (fourth control device) according to the fourth embodiment of the present invention.

  Hereinafter, an air-fuel ratio control apparatus for an internal combustion engine (hereinafter also simply referred to as “control apparatus”) according to each embodiment of the present invention will be described with reference to the drawings. This control device is also a part of the fuel injection amount control device that controls the fuel injection amount (fuel supply amount) contained in the air-fuel mixture supplied to the internal combustion engine.

<First Embodiment>
(Constitution)
FIG. 1 shows a system in which a control device according to the first embodiment (hereinafter also referred to as “first control device”) is applied to a 4-cycle, spark ignition type, multi-cylinder (in-line 4-cylinder) internal combustion engine 10. The schematic structure of is shown. Internal combustion engine 10 includes an engine body 20, an intake system 30, and an exhaust system 40.

  The engine body portion 20 includes a cylinder block portion and a cylinder head portion. The engine body 20 includes a plurality of cylinders (combustion chambers) 21. Each cylinder communicates with an “intake port and exhaust port” (not shown). A communicating portion between the intake port and the combustion chamber 21 is opened and closed by an intake valve (not shown). A communicating portion between the exhaust port and the combustion chamber 21 is opened and closed by an exhaust valve (not shown). Each combustion chamber 21 is provided with a spark plug (not shown).

  The intake system 30 includes an intake manifold 31, an intake pipe 32, a plurality of fuel injection valves 33, and a throttle valve 34.

  The intake manifold 31 includes a plurality of branch portions 31a and a surge tank 31b. One end of each of the plurality of branch portions 31a is connected to each of the plurality of intake ports. The other ends of the plurality of branch portions 31a are connected to the surge tank 31b.

  One end of the intake pipe 32 is connected to the surge tank 31b. An air filter (not shown) is disposed at the other end of the intake pipe 32.

  One fuel injection valve 33 is provided for each cylinder (combustion chamber) 21. The fuel injection valve 33 is provided at the intake port. Fuel is supplied to the fuel injection valve 33 from a fuel tank (not shown) through the fuel pipe 50. The fuel injection valve 33 opens in response to the injection instruction signal, and puts “the fuel of the indicated fuel injection amount included in the injection instruction signal” into the intake port (therefore, the cylinder 21 corresponding to the fuel injection valve 33). It comes to inject.

  The throttle valve 34 is rotatably disposed in the intake pipe 32. The throttle valve 34 has a variable opening cross-sectional area of the intake passage. The throttle valve 34 is rotationally driven in the intake pipe 32 by a throttle valve actuator (not shown).

  The exhaust system 40 includes an exhaust manifold 41, an exhaust pipe 42, an upstream catalyst 43 disposed in the exhaust pipe 42, and a “downstream catalyst (not shown) disposed in the exhaust pipe 42 downstream of the upstream catalyst 43. Is provided.

  The exhaust manifold 41 includes a plurality of branch portions 41a and a collecting portion 41b. One end of each of the plurality of branch portions 41a is connected to each of the plurality of exhaust ports. The other ends of the plurality of branch portions 41a are gathered in the gathering portion 41b. The collecting portion 41b is also referred to as an exhaust collecting portion HK because exhaust gas discharged from a plurality of (two or more, four in this example) cylinders gathers.

  The exhaust pipe 42 is connected to the collecting portion 41b. The exhaust port, the exhaust manifold 41 and the exhaust pipe 42 constitute an exhaust passage.

Each of the upstream side catalyst 43 and the downstream side catalyst is a so-called three-way catalyst device (exhaust purification catalyst) carrying an active component made of a noble metal (catalyst substance) such as platinum, rhodium and palladium. Each catalyst oxidizes unburned components such as HC, CO, and H ₂ when the air-fuel ratio of the gas flowing into each catalyst is “the air-fuel ratio within the window of the three-way catalyst (for example, the theoretical air-fuel ratio)”. In addition, it has a function of reducing nitrogen oxides (NOx). This function is also called a catalyst function.

  Further, each catalyst has an oxygen storage function for storing (storing) oxygen. That is, each catalyst occludes oxygen and purifies NOx when excessive oxygen is contained in the gas flowing into the catalyst (catalyst inflow gas). When the catalyst inflow gas contains excessive unburned substances, each catalyst releases the stored oxygen and purifies the unburned substances. Each catalyst releases more oxygen as the air-fuel ratio of the catalyst inflow gas decreases. In a state in which more oxygen is released (in other words, a state in which the concentration of the reducing agent in the catalyst is high), the catalyst can reduce NOx at a higher reaction rate.

The oxygen storage function of the catalyst is provided by an oxygen storage material such as ceria (CeO ₂ ) supported on the catalyst. Each catalyst can purify unburned components and nitrogen oxides even if the air-fuel ratio shifts from the stoichiometric air-fuel ratio due to the oxygen storage function. That is, the window width is expanded by the oxygen storage function.

  This system includes a hot-wire air flow meter 61, a throttle position sensor 62, a water temperature sensor 63, a crank position sensor 64, an intake cam position sensor 65, an upstream air-fuel ratio sensor 66, a downstream air-fuel ratio sensor 67, and an accelerator opening sensor. 68.

  The air flow meter 61 outputs a signal corresponding to the mass flow rate (intake air flow rate) Ga of intake air flowing through the intake pipe 32. That is, the intake air amount Ga represents the intake air amount taken into the engine 10 per unit time.

  The throttle position sensor 62 detects the opening (throttle valve opening) of the throttle valve 34 and outputs a signal representing the throttle valve opening TA.

  The water temperature sensor 63 detects the temperature of the cooling water of the engine 10 and outputs a signal indicating the cooling water temperature THW. The coolant temperature THW is an operating state index amount that represents the warm-up state of the engine 10 (temperature of the engine 10).

  The crank position sensor 64 outputs a signal having a narrow pulse every time the crankshaft rotates 10 ° and a wide pulse every time the crankshaft rotates 360 °. This signal is converted into an engine speed NE by an electric control device 70 described later.

  The intake cam position sensor 65 outputs one pulse every time the intake cam shaft rotates 90 degrees, 90 degrees, and 180 degrees from a predetermined angle. The electric control device 70 described later acquires an absolute crank angle CA based on the compression top dead center of the reference cylinder (for example, the first cylinder) based on signals from the crank position sensor 64 and the intake cam position sensor 65. It has become. This absolute crank angle CA is set to “0 ° crank angle” at the compression top dead center of the reference cylinder, and increases to a 720 ° crank angle according to the rotation angle of the crankshaft. Set to

  The upstream air-fuel ratio sensor 66 is disposed in “one of the exhaust manifold 41 and the exhaust pipe 42” at a position between the collecting portion 41 b (exhaust collecting portion HK) of the exhaust manifold 41 and the upstream catalyst 43. .

  The upstream air-fuel ratio sensor 66 is disclosed in, for example, “Limit current type wide area air-fuel ratio including diffusion resistance layer” disclosed in JP-A-11-72473, JP-A-2000-65782, JP-A-2004-69547, and the like. Sensor ".

  The upstream air-fuel ratio sensor 66 corresponds to the air-fuel ratio of the exhaust gas flowing through the position where the upstream air-fuel ratio sensor 66 is disposed (the air-fuel ratio of the “catalyst inflow gas” that is the gas flowing into the catalyst 43, the upstream air-fuel ratio abyfs). Output the output value Vabyfs. As shown in FIG. 2, the output value Vabyfs increases as the air-fuel ratio (upstream air-fuel ratio abyfs) of the catalyst inflow gas increases (as the air-fuel ratio becomes leaner).

  The electric control device 70 stores an air-fuel ratio conversion table (map) Mapabyfs that defines the relationship shown in FIG. 2 between the output value Vabyfs and the upstream air-fuel ratio abyfs. The electric control device 70 detects the actual upstream air-fuel ratio abyfs (obtains the detected upstream air-fuel ratio abyfs) by applying the output value Vabyfs to the air-fuel ratio conversion table Mapabyfs.

  Referring to FIG. 1 again, the downstream air-fuel ratio sensor 67 is disposed in the exhaust pipe 42. The downstream air-fuel ratio sensor 67 is disposed downstream of the upstream catalyst 43 and upstream of the downstream catalyst (that is, the exhaust passage between the upstream catalyst 43 and the downstream catalyst). It is. The downstream air-fuel ratio sensor 67 is a known electromotive force type oxygen concentration sensor (a known concentration cell type oxygen concentration sensor using a solid electrolyte such as stabilized zirconia). The downstream air-fuel ratio sensor 67 generates an output value Voxs corresponding to the air-fuel ratio of the gas to be detected, which is a gas passing through a portion of the exhaust passage where the downstream air-fuel ratio sensor 67 is disposed. ing. In other words, the output value Voxs is a value corresponding to the air-fuel ratio of the gas flowing out from the upstream catalyst 43 and flowing into the downstream catalyst.

  As shown in FIG. 3, the output value Voxs becomes the maximum output value max (for example, about 0.9 V to 1.0 V) when the air-fuel ratio of the detected gas is richer than the stoichiometric air-fuel ratio. The output value Voxs becomes the minimum output value min (for example, about 0.1 V to 0 V) when the air-fuel ratio of the gas to be detected is leaner than the stoichiometric air-fuel ratio. Further, the output value Voxs is a voltage Vst (median value Vmid, intermediate voltage Vst, for example, about 0.5 V) between the maximum output value max and the minimum output value min when the air-fuel ratio of the gas to be detected is the stoichiometric air-fuel ratio. ) The output value Voxs suddenly changes from the maximum output value max to the minimum output value min when the air-fuel ratio of the gas to be detected changes from an air-fuel ratio richer than the stoichiometric air-fuel ratio to a lean air-fuel ratio. Similarly, the output value Voxs suddenly changes from the minimum output value min to the maximum output value max when the air-fuel ratio of the detected gas changes from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to a rich air-fuel ratio.

  The accelerator opening sensor 68 shown in FIG. 1 outputs a signal representing the operation amount Accp (accelerator pedal operation amount, accelerator pedal AP opening amount) of the accelerator pedal AP operated by the driver. The accelerator pedal operation amount Accp increases as the operation amount of the accelerator pedal AP increases.

  The electric control device 70 includes: “a CPU, a program executed by the CPU, a ROM in which tables (maps, functions), constants, and the like are stored in advance; a RAM in which the CPU temporarily stores data as necessary; RAM), an interface including an AD converter, and the like ".

  The backup RAM is supplied with electric power from a battery mounted on the vehicle regardless of the position of an ignition key switch (not shown) of the vehicle on which the engine 10 is mounted (any one of an off position, a start position, an on position, etc.). It is like that. When receiving power from the battery, the backup RAM stores data according to an instruction from the CPU (data is written) and holds (stores) the data so that the data can be read. Therefore, the backup RAM can hold data even when the operation of the engine 10 is stopped.

  The backup RAM cannot retain data when the power supply from the battery is interrupted, for example, when the battery is removed from the vehicle. Therefore, when the power supply to the backup RAM is resumed, the CPU initializes (sets to the default value) data to be held in the backup RAM. The backup RAM may be a readable / writable nonvolatile memory such as an EEPROM.

  The electric control device 70 is connected to the above-described sensors and the like, and supplies signals from these sensors to the CPU. Further, the electric control device 70 is responsive to an instruction from the CPU to provide a spark plug (actually an igniter) provided for each cylinder, a fuel injection valve 33 provided for each cylinder, and a throttle. A drive signal (instruction signal) is sent to a valve actuator or the like.

  The electric control device 70 sends an instruction signal to the throttle valve actuator so that the throttle valve opening TA increases as the acquired accelerator pedal operation amount Accp increases. That is, the electric control device 70 changes the opening degree of the “throttle valve 34 disposed in the intake passage of the engine 10” according to the acceleration operation amount (accelerator pedal operation amount Accp) of the engine 10 changed by the driver. Throttle valve drive means is provided.

(Outline of operation of first control device)
Based on the output value Voxs of the downstream air-fuel ratio sensor 67, the first control device determines whether the state of the catalyst 43 (oxygen storage state) is an oxygen excess state or an oxygen deficiency state.
The oxygen excess state is also referred to as a lean state. The oxygen excess state is a state in which the oxygen storage amount of the catalyst 43 tends to be excessive and is approaching a value close to the maximum oxygen storage amount Cmax.
The oxygen-deficient state is also called a rich state. The oxygen-deficient state is a state where the oxygen storage amount of the catalyst 43 tends to be insufficient and is becoming a value close to “0”.

  More specifically, the first control device is a case where it is determined that the state of the catalyst 43 is an oxygen excess state, and the change amount ΔVoxs per predetermined time of the output value Voxs is a positive value. When the magnitude | ΔVoxs | becomes larger than the rich determination threshold dRichth, it is determined that the state of the catalyst 43 has become an oxygen-deficient state. At this time, the first control device sets the value of the catalyst lean state display flag XCCROLean to “0”.

  Furthermore, when it is determined that the state of the catalyst 43 is in an oxygen-deficient state, the first control device has a negative change amount ΔVoxs and the magnitude | ΔVoxs | is less than the lean determination threshold dLeanth. Is also increased, it is determined that the state of the catalyst 43 has become an oxygen-excess state. At this time, the first control device sets the value of the catalyst lean state display flag XCCROLean to “1”.

  In the first control device, when it is determined that the state of the catalyst 43 is an excess oxygen state, and the output value Voxs is greater than the rich determination threshold VRichth, the state of the catalyst 43 is insufficient for oxygen. It may be determined that the state has been reached. Further, the first control device determines that the state of the catalyst 43 is an oxygen-excess state when the output value Voxs becomes smaller than the lean determination threshold value VLeanth when the state of the catalyst 43 is determined to be an oxygen-deficient state. It may be determined that it has become.

  When the state of the catalyst 43 is an oxygen-excess state, an excessive unburned material should flow into the catalyst 43. Therefore, when the first control device determines that the state of the catalyst 43 is an excess oxygen state (when the value of the catalyst lean state display flag XCCROLean is set to “1”), the value of the rich request flag XRichreq is set to “1”. (The target air-fuel ratio abyfr, which is the target of the air-fuel ratio of the air-fuel mixture supplied to the engine) is changed to "the target rich air-fuel ratio afRich smaller than the stoichiometric air-fuel ratio" Set. The target air-fuel ratio abyfr is also a target for the air-fuel ratio of the exhaust gas flowing into the catalyst 43.

  On the other hand, when the state of the catalyst 43 is an oxygen-deficient state, excess oxygen should flow into the catalyst 43. Therefore, when the first controller determines that the state of the catalyst 43 is an oxygen-deficient state (when the value of the catalyst lean state display flag XCCROLean is set to “0”), the value of the rich request flag XRichreq is set to “0”. Is set (determined that a lean request has occurred), and the target air-fuel ratio abyfr is set to “a target lean air-fuel ratio afLean larger than the theoretical air-fuel ratio”.

Further, the first control device determines whether or not an operation state in which a large amount of nitrogen oxide flows into the catalyst 43 is predicted to arrive. Specifically, the first control device has a large amount of nitrogen oxides in the catalyst 43 when all the conditions described below (hereinafter simply referred to as “predetermined conditions” or “specific conditions”) are satisfied. Predict that the inflowing operating state will arrive.
(Condition 1) The intake air amount Ga is larger than the low-side air amount threshold GaLoth and smaller than the high-side air amount threshold GaHith. The high side air amount threshold GaHith is larger than the low side air amount threshold GaLoth.
(Condition 2) The amount of change (| ΔGa |) per unit time of the intake air amount Ga is smaller than the predetermined change amount threshold ΔGath.

Note that the intake air amount Ga in the conditions 1 and 2 can be replaced with the load KL, the throttle valve opening degree TA, the accelerator pedal operation amount Accp, and the like. These are all parameters that increase as the intake air amount Ga increases, and are also referred to as intake air amount correlation values. The load KL is a load factor (filling rate) KL in this example, and is calculated based on the following equation (1). In this equation (1), Mc (k) is the amount of air that a cylinder inhales in one intake stroke (unit: (g)), ρ is air density (unit: (g / l)), L is engine 10 is the displacement (unit is (l)), and 4 is the number of cylinders of the engine 10.

KL = {Mc (k) / (ρ · L / 4)} · 100 (%) (1)

  Further, the condition 1 is that “the speed of the vehicle on which the engine 10 is mounted is larger than the“ low speed threshold ”and smaller than the“ high speed threshold larger than the low speed threshold ”. May be replaced by the condition “

  When the predetermined condition is not satisfied (that is, when at least one of the condition 1 and the condition 2 is not satisfied), the first control apparatus performs the target lean air-fuel ratio as shown before time t1 in FIG. afLean is set to the reference target lean air-fuel ratio afLean0, and the target rich air-fuel ratio afRich is set to the reference target rich air-fuel ratio afRich0. The reference target lean air-fuel ratio afLean0 is an air-fuel ratio that is larger by a predetermined positive value A than the theoretical air-fuel ratio. The reference target rich air-fuel ratio afRich0 is an air-fuel ratio that is smaller by a predetermined positive value A than the theoretical air-fuel ratio. Therefore, the average value of the reference target lean air-fuel ratio afLean0 and the reference target rich air-fuel ratio afRich0 is the stoichiometric air-fuel ratio stoich.

  On the other hand, when the predetermined condition is satisfied (that is, when both the condition 1 and the condition 2 are satisfied), the first control device, as shown after time t1 in FIG. The lean air-fuel ratio afLean is set to “a value that is smaller than the reference target lean air-fuel ratio afLean0 by a predetermined positive value ΔL (afLean0−ΔL)”, and the target rich air-fuel ratio afRich is set to a value that is more positive than the reference target rich air-fuel ratio afRich0. The value is set to a value (afRich0−ΔR) that is smaller by the value ΔR ”. However, the value (afLean0−ΔL) is larger than the stoichiometric air-fuel ratio stoich.

  Thereby, since the average of the air-fuel ratio of the exhaust gas flowing into the catalyst 43 is “smaller than the stoichiometric air-fuel ratio stoich”, the concentration of the reducing agent in the catalyst 43 increases after time t1 as compared to before time t1. Therefore, when the engine 10 is subsequently accelerated and a large amount of NOx flows into the catalyst 43, the reduction rate of NOx in the catalyst 43 is sufficiently high, so the amount of unpurified NOx flowing out from the catalyst 43 is reduced. can do.

(Actual operation)
Next, the actual operation of the first control device will be described.

<Fuel injection control>
The CPU of the first control device repeatedly executes the fuel injection control routine shown in FIG. 5 for each cylinder every time the crank angle of any cylinder reaches a predetermined crank angle before the intake top dead center. It has become. The predetermined crank angle is, for example, BTDC 90 ° CA (90 ° crank angle before intake top dead center). A cylinder whose crank angle coincides with the predetermined crank angle is also referred to as a “fuel injection cylinder”. The CPU calculates the commanded fuel injection amount (final fuel injection amount) Fi and instructs fuel injection by this fuel injection control routine.

  When the crank angle of any cylinder coincides with the predetermined crank angle before the intake top dead center, the CPU starts the process from step 500 and proceeds to step 505 to “intake air amount Ga, engine rotational speed NE, and lookup. Based on the table “MapMc (Ga, NE)”, “the amount of air taken into the fuel injection cylinder (ie, the cylinder intake air amount) Mc)” is acquired. The in-cylinder intake air amount Mc may be calculated by a well-known air model (a model constructed according to a physical law simulating the behavior of air in the intake passage).

  Next, the CPU proceeds to step 510 to determine whether or not the value of the feedback control flag XFB is “1”. The value of the feedback control flag XFB is set to “1” when the air-fuel ratio feedback control condition is satisfied, and is set to “0” when the feedback control condition is not satisfied. Further, the value of the feedback control flag XFB is set to “0” in the initial routine. The initial routine is a routine that is executed by the CPU when the ignition key switch of the vehicle on which the engine 10 is mounted is changed from the off position to the on position.

The air-fuel ratio feedback control condition is satisfied, for example, when all of the following conditions are satisfied.
(A1) The upstream air-fuel ratio sensor 66 is activated.
(A2) The downstream air-fuel ratio sensor 67 is activated.
(A3) The engine load KL is equal to or less than the threshold load KLfbth.

  If the value of the feedback control flag XFB is not “1”, the CPU makes a “No” determination at step 510 to proceed to step 515 to set the target air-fuel ratio abyfr to the stoichiometric air-fuel ratio stoich (eg, 14.6). To do.

  Next, the CPU sequentially performs the processing from step 520 to step 535 described below, proceeds to step 595, and once ends this routine.

  Step 520: The CPU calculates the basic fuel injection amount Fbase by dividing the in-cylinder intake air amount Mc by the target air-fuel ratio abyfr. The basic fuel injection amount Fbase is a feed-forward amount of the fuel injection amount necessary for making the air-fuel ratio of the engine coincide with the target air-fuel ratio abyfr.

  Step 525: The CPU reads the main feedback amount KFmain separately calculated by a routine not shown. The main feedback amount KFmain is calculated based on known PID control so that the detected upstream air-fuel ratio abyfs matches the target air-fuel ratio abyfr. Therefore, the main feedback amount KFmain is increased when the detected upstream air-fuel ratio abyfs is larger than the target air-fuel ratio abyfr, and is decreased when the detected upstream air-fuel ratio abyfs is smaller than the target air-fuel ratio abyfr. The main feedback amount KFmain is set to “1” when the value of the feedback control flag XFB is “0”. Further, the main feedback amount KFmain may always be set to “1”. That is, feedback control using the main feedback amount KFmain is not essential in this embodiment.

  Step 530: The CPU calculates the command fuel injection amount Fi by correcting the basic fuel injection amount Fbase with the main feedback amount KFmain. More specifically, the CPU calculates the command fuel injection amount Fi by multiplying the basic fuel injection amount Fbase by the main feedback amount KFmain.

  Step 535: The CPU sends to the fuel injection valve 33 an injection instruction signal for injecting “the fuel of the indicated fuel injection amount Fi” from the “fuel injection valve 33 provided corresponding to the fuel injection cylinder”. To do.

  As a result, an amount of fuel required to make the air-fuel ratio of the engine coincide with the target air-fuel ratio abyfr is injected from the fuel injection valve 33 of the fuel injection cylinder. In other words, Step 520 to Step 535 are the command fuel injection amount control means for “controlling the command fuel injection amount Fi so that the air / fuel ratio of the engine matches the target air / fuel ratio abyfr” or “the fuel supplied to the engine 10”. A fuel supply amount control means for controlling the amount based on the set target air-fuel ratio abyfr.

  On the other hand, if the value of the feedback control flag XFB is “1” at the time when the CPU performs the process of step 510, the CPU determines “Yes” in step 510 and proceeds to step 540, where the rich request flag XRichreq It is determined whether or not the value of “1” is “1”. The value of the rich request flag XRichreq is set by a routine shown in FIG.

  If the value of the rich request flag XRichreq is “1”, the CPU makes a “Yes” determination at step 540 to proceed to step 545 to read out the target rich air-fuel ratio afRich. The target rich air-fuel ratio afRich is separately calculated by a routine shown in FIG. Next, the CPU proceeds to step 550 and sets the target air-fuel ratio abyfr to the target rich air-fuel ratio afRich. Thereafter, the CPU proceeds to step 520 and subsequent steps. Accordingly, the air-fuel ratio of the engine is made to coincide with the target rich air-fuel ratio afRich.

  On the other hand, if the value of the rich request flag XRichreq is “0” at the time when the CPU executes the process of step 540, the CPU makes a “No” determination at step 540 to proceed to step 555, where the target lean Read the air-fuel ratio afLean. The target lean air-fuel ratio afLean is also separately calculated by a routine shown in FIG. Next, the CPU proceeds to step 560 to set the target air / fuel ratio abyfr to the target lean air / fuel ratio afLean. Thereafter, the CPU proceeds to step 520 and subsequent steps. Accordingly, the air-fuel ratio of the engine is made to coincide with the target lean air-fuel ratio afLean.

<Catalyst state determination>
The CPU repeatedly executes the “catalyst state determination routine” shown in the flowchart of FIG. 6 every elapse of a predetermined time ts. Accordingly, when the predetermined timing comes, the CPU starts the process from step 600 and proceeds to step 605, from “current output value Voxs of downstream air-fuel ratio sensor 67” to “previous output value of downstream air-fuel ratio sensor 67. By subtracting “Voxsold”, the change amount ΔVoxs of the output value Voxs per predetermined time ts (unit time) is calculated.

  Next, the CPU proceeds to step 610 to store the current output value Voxs as “previous output value Voxsold”. That is, the previous output value Voxsold is the output value Voxs at the time point before the current time by the predetermined time ts (the output value Voxs when this routine was executed last time). The change amount ΔVoxs is also referred to as a change rate ΔVoxs.

  Next, the CPU proceeds to step 615 to read the rich determination threshold value dRichth. The rich determination threshold value dRichth is set to a constant value in this example. Next, the CPU proceeds to step 620 to read the lean determination threshold value dLeanth. The lean determination threshold value dLeanth is set to a constant value in this example.

  Next, the CPU proceeds to step 630 to determine whether or not the value of the catalyst lean state display flag XCCROLean is “1”. The value of the catalyst lean state display flag XCCROLean is set to “1” in the above-described initial routine. Further, the value of the catalyst lean state display flag XCCROLean is set to “0” when it is determined that the state of the catalyst 43 is an oxygen deficient state (rich state) based on the output value Voxs of the downstream air-fuel ratio sensor 67. Then, it is set to “1” when it is determined that the state of the catalyst 43 is the oxygen excess state (lean state) based on the output value Voxs of the downstream side air-fuel ratio sensor 67.

  Assume that the value of the catalyst lean state display flag XCCROLean is “1”. In this case, the CPU makes a “Yes” determination at step 630 to proceed to step 640 to determine whether or not the change speed ΔVoxs is positive. That is, the CPU determines whether or not the output value Voxs is increasing. At this time, if the change speed ΔVoxs is not positive, the CPU makes a “No” determination at step 640 to directly proceed to step 695 to end the present routine tentatively.

  By the way, when the value of the catalyst lean state display flag XCCROLean is “1”, the value of the rich request flag XRichreq is set to “1” by the routine shown in FIG. 7 to be described later, whereby the target air-fuel ratio abyfr is set to the target rich. The air-fuel ratio is set to afRich (see step 540 to step 550 in FIG. 5). Therefore, the oxygen storage amount of the catalyst 43 gradually decreases, and unburned substances begin to flow out of the catalyst 43 from a certain point.

  As a result, the change rate ΔVoxs becomes a positive value. When the change speed ΔVoxs becomes a positive value, the CPU makes a “Yes” determination at step 640 to proceed to step 650 to determine whether or not the magnitude | ΔVoxs | of the change speed ΔVoxs is greater than the rich determination threshold dRichth. To do. At this time, if the magnitude | ΔVoxs | is equal to or smaller than the rich determination threshold dRichth, the CPU makes a “No” determination at step 650 to directly proceed to step 695 to end the present routine tentatively.

  If the magnitude | ΔVoxs | of the change speed ΔVoxs is larger than the rich determination threshold value dRichth at the time when the CPU executes the process of step 650, the CPU determines “Yes” in step 650 and proceeds to step 660. The value of the catalyst lean state display flag XCCROLean is set to “0”. That is, when the output value Voxs increases and the magnitude | ΔVoxs | of the change rate ΔVoxs is larger than the rich determination threshold value dRichth, the CPU determines that “the state of the catalyst 43 is an oxygen-deficient state”. The value of the catalyst lean state display flag XCCROLean is set to “0”.

  In this state (that is, in a state where the value of the catalyst lean state display flag XCCROLean is set to “0”), when the CPU starts again from step 600, the CPU proceeds to step 630 via step 605 to step 620. In step 630, the determination is “No”, and the process proceeds to step 670.

  In step 670, the CPU determines whether the change speed ΔVoxs is negative. That is, the CPU determines whether or not the output value Voxs is decreasing. At this time, if the change speed ΔVoxs is not negative, the CPU makes a “No” determination at step 670 to directly proceed to step 695 to end the present routine tentatively.

  By the way, when the value of the catalyst lean state display flag XCCROLean is “0”, the value of the rich request flag XRichreq is set to “0” by the routine shown in FIG. 7 described later, whereby the target air-fuel ratio abyfr becomes the target lean. The air-fuel ratio is set to afLean (see Step 540, Step 555, and Step 560 in FIG. 5). Accordingly, the oxygen storage amount of the catalyst 43 gradually increases, and oxygen begins to flow out of the catalyst 43 from a certain point.

  As a result, the change rate ΔVoxs becomes a negative value. When the change speed ΔVoxs becomes a negative value, the CPU makes a “Yes” determination at step 670 to proceed to step 680 to determine whether or not the magnitude | ΔVoxs | of the change speed ΔVoxs is greater than the lean determination threshold dLeanth. To do. At this time, if the magnitude | ΔVoxs | is equal to or smaller than the lean determination threshold value dLeanth, the CPU makes a “No” determination at step 680 to directly proceed to step 695 to end the present routine tentatively.

  On the other hand, when the magnitude | ΔVoxs | of the change speed ΔVoxs is larger than the lean determination threshold value dLeanth, the CPU makes a “Yes” determination at step 680 to proceed to step 690 to set the value of the catalyst lean state display flag XCCROLean. Set to “1”. That is, when the output value Voxs is decreasing and the magnitude | ΔVoxs | of the change speed ΔVoxs is larger than the lean determination threshold value dLeanth, the CPU determines that “the state of the catalyst 43 is an oxygen excess state”. The catalyst lean state display flag XCCROLean is set to “1”.

  The CPU sets the value of the catalyst lean state display flag XCCROLean to “0” when the value of the catalyst lean state display flag XCCROLean is “1” and the output value Voxs becomes larger than the rich determination threshold VRichth. May be. Similarly, when the value of the catalyst lean state display flag XCCROLean is “0” and the output value Voxs becomes smaller than the lean determination threshold value VLeanth, the value of the catalyst lean state display flag XCCROLean is set to “1”. Also good. In this case, the rich determination threshold value VRichth may be a value equal to or less than the median value Vmid. The lean determination threshold value VLeanth may be a value equal to or greater than the median value Vmid.

  As described above, the value of the catalyst lean state display flag XCCROLean is alternately set to one of “1” and “0” based on the output value Voxs of the downstream air-fuel ratio sensor 67. Then, the rich request flag XRichreq is set according to the catalyst lean state display flag XCCROLean, and the target air-fuel ratio abyfr is determined according to the rich request flag XRichreq.

<Rich request flag setting (determination of required air-fuel ratio)>
The CPU executes the required air-fuel ratio determination routine shown in FIG. 7 every elapse of a predetermined time. Accordingly, when the predetermined timing comes, the CPU starts the process from step 700 and proceeds to step 710 to determine whether or not the value of the catalyst lean state display flag XCCROLean is “1”. At this time, if the value of the catalyst lean state display flag XCCROLean is “1”, the CPU proceeds to step 720 and sets the value of the rich request flag XRichreq to “1”. That is, the CPU determines that the “required air-fuel ratio” is a rich air-fuel ratio and that a rich request has occurred. Thereafter, the CPU proceeds to step 795 to end the present routine tentatively.

  In contrast, if the value of the catalyst lean state display flag XCCROLean is “0” at the time when the CPU executes the process of step 710, the CPU proceeds to step 730 and sets the value of the rich request flag XRichreq to “0”. Set. That is, the CPU determines that the “required air-fuel ratio” is a lean air-fuel ratio and a lean request has occurred. Thereafter, the CPU proceeds to step 795 to end the present routine tentatively.

<Calculation of target air-fuel ratio>
The CPU executes the target air-fuel ratio calculation routine shown in FIG. 8 every elapse of a predetermined time. Accordingly, when the predetermined timing is reached, the CPU starts the process from step 800 and proceeds to step 805 to determine whether or not the above-described condition 1 is satisfied. That is, the CPU determines whether or not the intake air amount Ga is larger than the low-side air amount threshold GaLoth and smaller than the high-side air amount threshold GaHith.

  Now, assume that the determination condition of step 805 is not satisfied. In this case, the CPU makes a “No” determination at step 805 to sequentially perform the processes of step 810 and step 815 described below, and then proceeds to step 895 to end the present routine tentatively.

Step 810: The CPU sets the value of the target rich air-fuel ratio afRich to the reference target rich air-fuel ratio afRich0. The reference target rich air-fuel ratio afRich0 is a value (for example, 14.2) smaller than the theoretical air-fuel ratio stoich by a positive predetermined value A.
Step 815: The CPU sets the value of the target lean air-fuel ratio afLean to the reference target lean air-fuel ratio afLean0. The reference target lean air-fuel ratio afLean0 is a value (for example, 15.0) larger by a predetermined positive value A than the stoichiometric air-fuel ratio stoich.

  On the other hand, if the intake air amount Ga is larger than the low-side air amount threshold GaLoth and smaller than the high-side air amount threshold GaHith at the time when the CPU executes the process of step 805, the CPU The process proceeds to step 820, and the intake air amount change amount ΔGa per predetermined time ts (unit time) is calculated by subtracting the “previous intake air amount Gaold” from the “current intake air amount Ga”. To do.

  Next, the CPU proceeds to step 825 to store the current intake air amount Ga as “previous intake air amount Gaold”. That is, the previous intake air amount Gaold is the intake air amount Ga at a time point a predetermined time ts before the current time (the intake air amount Ga when this routine was executed last time).

  Next, the CPU proceeds to step 830 to determine whether or not the magnitude | ΔGa | of the intake air amount change amount ΔGa is smaller than a predetermined change amount threshold value ΔGath. That is, the CPU determines whether or not the condition 2 is satisfied. At this time, if the magnitude | ΔGa | is equal to or greater than the change amount threshold value ΔGath, the CPU makes a “No” determination at step 830 to execute the processing of step 810 and step 815 to end the present routine tentatively. Accordingly, in this case, the target rich air-fuel ratio afRich is set to the reference target rich air-fuel ratio afRich0, and the target lean air-fuel ratio afLean is set to the reference target lean air-fuel ratio afLean0.

  On the other hand, when the CPU executes the process of step 830, if the magnitude | ΔGa | of the intake air amount change amount ΔGa is smaller than the predetermined change amount threshold value ΔGath, the CPU determines “Yes” in step 830. And the processing of step 835 to step 850 described below is performed in order, and then the routine proceeds to step 895 to end the present routine tentatively.

Step 835: The CPU determines a target rich air-fuel ratio correction amount ΔR based on the intake air amount Ga. The target rich air-fuel ratio correction amount ΔR is determined so as to increase as the intake air amount Ga increases.
Step 840: The CPU sets the target rich air-fuel ratio afRich to a value (afRich0−ΔR) obtained by subtracting the target rich air-fuel ratio correction amount ΔR from the reference target rich air-fuel ratio afRich0. As a result, the target rich air-fuel ratio afRich is calculated as an air-fuel ratio that decreases as the intake air amount Ga increases, away from the stoichiometric air-fuel ratio stoich.

Step 845: The CPU determines a target lean air-fuel ratio correction amount ΔL based on the intake air amount Ga. The target lean air-fuel ratio correction amount ΔL is determined so as to increase as the intake air amount Ga increases.
Step 850: The CPU sets the target lean air-fuel ratio afLean to a value (afLean0−ΔL) obtained by subtracting the target lean air-fuel ratio correction amount ΔL from the reference target lean air-fuel ratio afLean0. As a result, the target lean air-fuel ratio afLean is calculated as an air-fuel ratio that decreases as the intake air amount Ga increases so as to approach the stoichiometric air-fuel ratio stoich. However, the target lean air-fuel ratio correction amount ΔL is determined such that the value (afLean0−ΔL) is larger than the stoichiometric air-fuel ratio stoich.

  As described above, according to the first control device, when the predetermined condition (condition 1 and condition 2) is satisfied (that is, it is determined as “Yes” in both step 805 and step 830). A large amount of NOx is predicted to flow into the catalyst 43.

  Then, according to the first control device, the target lean air-fuel ratio afLean is decreased by the target lean air-fuel ratio correction amount ΔL as compared with “when the predetermined condition is not satisfied” (step 845 and FIG. 8). In step 850), the target rich air-fuel ratio afRich is decreased by the target rich air-fuel ratio correction amount ΔR as compared to “when the predetermined condition is not satisfied” (steps 835 and 840 in FIG. 8). As a result, since the concentration of the reducing agent in the catalyst 43 is increased, the NOx reduction rate when NOx flows in increases. As a result, even when the engine 10 is accelerated thereafter and a large amount of NOx flows into the catalyst 43, the amount of unpurified NOx flowing out from the catalyst 43 can be reduced.

Second Embodiment
Next, a control device for an internal combustion engine according to a second embodiment of the present invention (hereinafter also referred to as “second control device”) will be described.

  When the predetermined condition is satisfied, the second control device sets a relative time for maintaining the target air-fuel ratio abyfr at the target rich air-fuel ratio afRich instead of changing the target rich air-fuel ratio afRich and the target lean air-fuel ratio afLean. This is different from the first control device only in that it is made longer.

  More specifically, like the first control device, the second control device sets the target air-fuel ratio abyfr to the target rich air-fuel ratio afRich when the value of the rich request flag XRichreq is “1”, and the rich request flag When the value of XRichreq is “0”, the target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean.

  Further, as shown in FIG. 9, the second control device determines that the lean delay time TDL is from the time (time t1, t5) when the value of the catalyst lean state display flag XCCROLean changes from “0” to “1”. When the time has elapsed, the rich request flag XRichreq is changed from “0” to “1”. In addition, the second control device performs the rich request flag XRichreq when the rich delay time TDR elapses from the time (time t3) when the value of the catalyst lean state display flag XCCROLean changes from “1” to “0”. Is changed from “1” to “0”. Therefore, by increasing the rich delay time TDR and / or by shortening the lean delay time TDL, the time during which the target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich is increased. The average value of the air-fuel ratio of the inflowing exhaust gas can be shifted to the rich side. Accordingly, the second control device increases the rich delay time TDR or shortens the lean delay time TDL when the predetermined condition is satisfied. Thereby, the second control device increases the concentration of the reducing agent in the catalyst 43 when the predetermined condition is satisfied.

(Actual operation)
The CPU of the second control device executes the routines shown in FIGS. 5 and 6 in the same manner as the CPU of the first control device. However, the target rich air-fuel ratio afRich read in step 545 in FIG. 5 is a constant value (for example, 14.2), and the target lean air-fuel ratio afLean read in step 555 in FIG. 5 is a constant value (15.0 ).

  Further, the CPU of the second control device executes the required air-fuel ratio determination routine shown in FIG. 10 every elapse of a predetermined time. Accordingly, when the predetermined timing comes, the CPU starts processing from step 1000 and proceeds to step 1010 to read the lean delay time TDL. The lean delay time TDL is calculated by a routine shown in FIG. Next, the CPU proceeds to step 1020 to read the rich delay time TDR. The rich delay time TDR is calculated by a routine shown in FIG.

  Next, the CPU proceeds to step 1030 to determine whether or not the value of the catalyst lean state display flag XCCROLean is “1”. At this time, if the value of the catalyst lean state display flag XCCROLean is “1”, the CPU makes a “Yes” determination at step 1030 to proceed to step 1040, where the value of the catalyst lean state display flag XCCROLean is “0”. It is determined whether or not the lean delay time TDL has elapsed since the time when the value changed to “1”.

  If the lean delay time TDL has not elapsed, the CPU makes a “No” determination at step 1040 to directly proceed to step 1095 to end the present routine tentatively. In this case, the value of the rich request flag XRichreq is not changed.

  On the other hand, if the lean delay time TDL has elapsed at the time when the CPU executes the process of step 1040, the CPU makes a “Yes” determination at step 1040 to proceed to step 1050, where the rich request flag XRichreq Is set to “1”. As a result, the target air-fuel ratio abyfr is changed from the target lean air-fuel ratio afLean to the target rich air after the lean delay time TDL has elapsed since the value of the catalyst lean state display flag XCCROLean has changed from “0” to “1”. The fuel ratio is changed to afRich. Thereafter, the CPU proceeds to step 1095 to end the present routine tentatively.

  On the other hand, when the value of the catalyst lean state display flag XCCROLean is “0” at the time when the CPU executes the process of step 1030, the CPU makes a “No” determination at step 1030 to proceed to step 1060. It is determined whether or not the rich delay time TDR has elapsed since the value of the lean state display flag XCCROLean has changed from “1” to “0”.

  If the rich delay time TDR has not elapsed, the CPU makes a “No” determination at step 1060 to directly proceed to step 1095 to end the present routine tentatively. In this case, the value of the rich request flag XRichreq is not changed.

  On the other hand, if the rich delay time TDR has elapsed at the time when the CPU executes the process of step 1060, the CPU makes a “Yes” determination at step 1060 to proceed to step 1070, where the rich request flag XRichreq Is set to “0”. As a result, the target air-fuel ratio abyfr is changed from the target rich air-fuel ratio afRich to the target lean air-space after the rich delay time TDR has elapsed since the value of the catalyst lean state display flag XCCROLean has changed from “1” to “0”. The fuel ratio is changed to afLean. Thereafter, the CPU proceeds to step 1095 to end the present routine tentatively.

  Further, the CPU executes the delay time calculation routine shown in FIG. 11 every elapse of a predetermined time. Note that the steps shown in FIG. 11 and also shown in FIG. 8 are denoted by the same reference numerals as the steps shown in FIG. Detailed description of these steps will be omitted as appropriate.

  If the predetermined condition described above is not satisfied, the CPU proceeds to step 1110 to set the rich delay time TDR to a certain reference rich delay time TDR0. Next, the CPU proceeds to step 1120, sets the lean delay time TDL to a constant reference lean delay time TDL0, proceeds to step 1195, and once ends this routine.

  On the other hand, if the predetermined condition described above is satisfied, the CPU proceeds to step 1130 to determine the rich delay time TDR based on the intake air amount Ga. More specifically, the rich delay time TDR is determined so as to increase in the range of the reference rich delay time TDR0 or more as the intake air amount Ga increases.

  Next, the CPU proceeds to step 1140 to determine the lean delay time TDL based on the intake air amount Ga. More specifically, the lean delay time TDL is determined so as to decrease in the range of the reference lean delay time TDL0 or less as the intake air amount Ga increases.

As described above, the second control device
When the change amount ΔVoxs per unit time of the output value Voxs of the downstream side air-fuel ratio sensor 67 is a negative value and the magnitude | ΔVoxs | becomes larger than the lean determination threshold value dLeanth, the state of the catalyst 43 is While determining that the oxygen excess state has occurred (steps 670 to 690 in FIG. 6), the change amount ΔVoxs is a positive value, and the magnitude | ΔVoxs | is greater than the rich determination threshold dRichth. At this time, it is determined that the state of the catalyst 43 is in an oxygen-deficient state (steps 640 to 650 in FIG. 6).

Further, the second control device includes target air-fuel ratio setting means, fuel supply amount control means for controlling the amount of fuel supplied to the engine based on the target air-fuel ratio set by the target air-fuel ratio setting means,
including.

The target air-fuel ratio setting means includes
When the catalyst state determination means determines that the state of the catalyst 43 has changed from the oxygen-deficient state to the oxygen-excess state, when “lean delay time TDL that is a predetermined delay time including 0” has elapsed. The target air-fuel ratio abyfr is set to “target rich air-fuel ratio afRich smaller than the stoichiometric air-fuel ratio” (steps 1040 and 1050 in FIG. 10 and steps 540 to 550 in FIG. 5), and the catalyst state determination means performs catalyst 43 The target air-fuel ratio abyfr is set to “theoretical sky” when the “rich delay time TDR that is a predetermined delay time including 0” has elapsed since it was determined that the state changed from the oxygen excess state to the oxygen deficiency state. The target lean air-fuel ratio afLean larger than the fuel ratio ”is set (steps 1060 and 1070 in FIG. 10 and step 54 in FIG. 5). 0, step 555 and step 560).
The fuel supply amount control means includes:
A fuel amount (fuel injection amount) supplied to the engine 10 is controlled based on the set target air-fuel ratio abyfr (steps 520 to 535, fuel injection valve 33 in FIG. 5).

  Further, the target air-fuel ratio setting means determines the rich delay time TDR when the predetermined condition is satisfied (see the determination of “Yes” in both steps 805 and 830 in FIG. 11). A time longer than the rich delay time TDR (= reference rich delay time TDR0) when the predetermined condition is not satisfied is configured (step 1130 in FIG. 11). When the rich delay time TDR is set in this way, the lean delay time TDL may always be “0” or a constant value.

  In addition, the target air-fuel ratio setting means determines the lean delay time TDL when the predetermined condition is satisfied (see the determination of “Yes” in both steps 805 and 830 in FIG. 11). The lean delay time TDL (= reference lean delay time TDL0) when the predetermined condition is not satisfied is set to be shorter (step 1140 in FIG. 11). When the lean delay time TDL is set in this way, the rich delay time TDR may be “0” or a constant value.

  Therefore, according to the second control apparatus, only the time when the target air-fuel ratio is set to the rich air-fuel ratio is “the time when the rich delay time TDR is increased” and / or “the time when the lean delay time TDL is shortened”. become longer. Therefore, the average value of the air-fuel ratio of the engine 10 (and hence the average value of the air-fuel ratio of the catalyst inflow gas that is the gas flowing into the catalyst) becomes smaller (rich) than the stoichiometric air-fuel ratio. Therefore, when the predetermined condition is satisfied, the state of the catalyst 43 can be set to “a state in which the NOx reduction rate is increased”.

<Third Embodiment>
Next, a control device for an internal combustion engine according to a third embodiment of the present invention (hereinafter also referred to as “third control device”) will be described.

  When the predetermined condition is satisfied, the third control device increases the rich determination threshold dRichth instead of changing the target rich air-fuel ratio afRich and the target lean air-fuel ratio afLean, so that the state of the catalyst 43 is in an oxygen excess state. This is different from the first control device only in that the period during which it is determined to be relatively long.

  More specifically, as with the first control device, the third control device sets the target air-fuel ratio abyfr to the target rich air-fuel ratio afRich when the value of the rich request flag XRichreq is “1”, and the rich request flag When the value of XRichreq is “0”, the target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean.

  Furthermore, as shown in FIG. 12, the third control device sets the rich determination threshold value dRichth to the reference rich determination threshold value dRichth0 when the predetermined condition described above is not satisfied. Therefore, in the example shown in FIG. 12, the values of the catalyst lean state display flag XCCROLean and the rich request flag XRichreq are changed from “1” to “0” at time t2. That is, when it is determined that the state of the catalyst 43 is an excess oxygen state, it is determined that the state of the catalyst 43 has changed to an oxygen-deficient state when the output value Voxs of the downstream air-fuel ratio sensor 67 slightly increases. At that time, the target air-fuel ratio abyfr is switched to the target lean air-fuel ratio afLean.

  On the other hand, when the predetermined condition described above is satisfied, the third control device sets the rich determination threshold value dRichth to “a value obtained by adding a positive correction amount ΔdRi to the reference rich determination threshold value dRichth0 (dRichth0 + ΔdRi)”. According to this, even when the output value Voxs of the downstream air-fuel ratio sensor 67 changes in the same manner, the values of the catalyst lean state display flag XCCROLean and the rich request flag XRichreq change from “1” to “0”. The time of change is time t3 later than time t2. That is, when it is determined that the state of the catalyst 43 is an excess oxygen state, the time t3 when the output value Voxs of the downstream air-fuel ratio sensor 67 increases by “an amount larger than the reference rich determination threshold dRichth0” per unit time. Is determined that the state of the catalyst 43 has changed to an oxygen-deficient state, and at that time, the target air-fuel ratio abyfr is switched to the target lean air-fuel ratio afLean. As a result, the target air-fuel ratio abyfr is set longer than the time corresponding to the period from time t2 to time t3, and is set to the target rich air-fuel ratio afRich. Accordingly, the third control device increases the concentration of the reducing agent in the catalyst 43 when the above-described predetermined condition is satisfied.

(Actual operation)
The CPU of the third control device executes the routines shown in FIGS. 5 to 7 in the same manner as the CPU of the first control device. However, the target rich air-fuel ratio afRich read in step 545 in FIG. 5 is a constant value (for example, 14.2), and the target lean air-fuel ratio afLean read in step 555 in FIG. 5 is a constant value (15.0 ).

  Further, the CPU of the third control device executes the determination threshold value calculation routine shown in FIG. 13 every elapse of a predetermined time. By this routine, the rich determination threshold value dRichth and the lean determination threshold value dLeanth that are read out in steps 615 and 620 in FIG. 6 are calculated. The steps shown in FIG. 13 and also shown in FIG. 8 are denoted by the same reference numerals as the steps shown in FIG. Detailed description of these steps will be omitted as appropriate.

  When the predetermined condition described above is not satisfied, the CPU proceeds to step 1310 in FIG. 13 to set the rich determination threshold dRichth to a constant reference rich determination threshold dRichth0. Next, the CPU proceeds to step 1320 to set the lean determination threshold value dLeanth to a certain reference lean determination threshold value dLeanth0, and proceeds to step 1395 to end the present routine tentatively.

  On the other hand, when the predetermined condition described above is satisfied, the CPU proceeds to step 1330 to determine the rich determination threshold dRichth based on the intake air amount Ga. More specifically, the rich determination threshold dRichth is determined so as to increase in a range equal to or greater than the reference rich determination threshold dRichth0 as the intake air amount Ga increases. In other words, the CPU obtains a positive correction amount ΔdRi that increases as the intake air amount Ga increases, and sets “a value obtained by adding the positive correction amount ΔdRi to the reference rich determination threshold dRichth0 (dRichth0 + ΔdRi)” as the rich determination threshold dRichth. To do.

  Next, the CPU proceeds to step 1340 to determine a lean determination threshold value dLeanth based on the intake air amount Ga. More specifically, the lean determination threshold value dLeanth is determined so as to decrease in a range equal to or less than the reference lean determination threshold value dLeanth0 as the intake air amount Ga increases. In other words, the CPU obtains a positive correction amount ΔdLi that increases as the intake air amount Ga increases, and calculates “a value obtained by subtracting the positive correction amount ΔdLi from the reference lean determination threshold value dLeanth0 (dLeanth0−ΔdLi)” as the lean determination threshold value dLeanth. Set as. Note that the lean determination threshold value dLeanth may be a constant value (a reference lean determination threshold value dLeanth0). Further, when the lean determination threshold value dLeanth is variable so as to be based on the processing in step 1340, the rich determination threshold value dRichth may be a constant value (reference rich determination threshold value dRichth0). Thereafter, the CPU proceeds to step 1395 to end the present routine tentatively.

  As described above, the third control device has the “target air-fuel ratio setting means and fuel supply amount control means” of the second control device. Further, the target air-fuel ratio setting means of the third control device uses the rich determination threshold value dRichth when the predetermined condition is satisfied as the rich determination threshold value dRichth when the predetermined condition is not satisfied (= The reference rich determination threshold value dRichth0) is set to a larger value (step 1330 in FIG. 13).

In addition, the target air-fuel ratio setting means of the third control device further includes:
The lean determination threshold value dLeanth when the predetermined condition is satisfied is smaller than the lean determination threshold value dLeanth (= reference lean determination threshold value dLeanth0) when the lean delay time is not satisfied. It is configured to set a value (step 1340 in FIG. 13).

  Therefore, according to the third control device, when the predetermined condition is satisfied, the period during which the state of the catalyst 43 is determined to be the oxygen-deficient state is shortened, and the state of the catalyst 43 is the oxygen-excess state. The period during which it is determined to be longer. Therefore, when the predetermined condition is satisfied, the time during which the target air-fuel ratio is set to the target rich air-fuel ratio afRich becomes relatively long. Therefore, the average value of the air-fuel ratio of the engine 10 (and hence the average value of the air-fuel ratio of the catalyst inflow gas that is the gas flowing into the catalyst) becomes smaller (rich) than the stoichiometric air-fuel ratio. Therefore, when the predetermined condition is satisfied, the state of the catalyst 43 can be set to “a state in which the NOx reduction rate is increased”.

<Fourth embodiment>
Next, a control device for an internal combustion engine according to a fourth embodiment of the present invention (hereinafter also referred to as “fourth control device”) will be described.

  Unlike the first to third control devices, the fourth control device controls the air-fuel ratio of the engine so that the temperature of the catalyst 43 rises when the predetermined condition is satisfied. More specifically, the fourth control device sets the target rich air-fuel ratio afRich when the predetermined condition is satisfied to a value smaller than the target rich air-fuel ratio afRich when the predetermined condition is not satisfied. In addition, the target lean air-fuel ratio afLean when the predetermined condition is satisfied is set to a value larger than the target lean air-fuel ratio afLean when the predetermined condition is not satisfied.

(Actual operation)
The CPU of the fourth control device executes the routines shown in FIGS. 5 to 7 in the same manner as the CPU of the first control device. Further, the CPU of the fourth control device executes the target air-fuel ratio calculation routine shown in FIG. 14 every elapse of a predetermined time. Note that the steps shown in FIG. 14 and the steps shown in FIG. 8 are also given the same reference numerals as the steps shown in FIG. Detailed description of these steps will be omitted as appropriate.

  When the predetermined condition described above is not satisfied, the CPU proceeds to step 810 in FIG. 14 to set the target rich air-fuel ratio afRich to a constant reference target rich air-fuel ratio afRich0. Next, the CPU proceeds to step 815 to set the target lean air-fuel ratio afLean to a constant reference target lean air-fuel ratio afLean0.

  On the other hand, when the predetermined condition described above is satisfied, the CPU sequentially performs the processes of steps 835 to 845 and step 1410 described below, and then proceeds to step 1495 to end the present routine tentatively.

  Step 835: The CPU determines a target rich air-fuel ratio correction amount ΔR based on the intake air amount Ga. The target rich air-fuel ratio correction amount ΔR is determined so as to increase as the intake air amount Ga increases.

  Step 840: The CPU sets the target rich air-fuel ratio afRich to a value (afRich0−ΔR) obtained by subtracting the target rich air-fuel ratio correction amount ΔR from the reference target rich air-fuel ratio afRich0. As a result, the target rich air-fuel ratio afRich is calculated as an air-fuel ratio that decreases as the intake air amount Ga increases, away from the stoichiometric air-fuel ratio stoich.

  Step 845: The CPU determines a target lean air-fuel ratio correction amount ΔL based on the intake air amount Ga. The target lean air-fuel ratio correction amount ΔL is determined so as to increase as the intake air amount Ga increases. In this case, the target lean air-fuel ratio correction amount ΔL for an arbitrary intake air amount Ga is determined as the same value as the target rich air-fuel ratio correction amount ΔR for the intake air amount Ga. However, the target lean air-fuel ratio correction amount ΔL for an arbitrary intake air amount Ga may be determined as a value different from the target rich air-fuel ratio correction amount ΔR for the intake air amount Ga.

  Step 1410: The CPU sets the target lean air-fuel ratio afLean to a value (afLean0 + ΔL) obtained by adding the target lean air-fuel ratio correction amount ΔL to the reference target lean air-fuel ratio afLean0. As a result, the target lean air-fuel ratio afLean is calculated as an air-fuel ratio that increases as the intake air amount Ga increases so as to move away from the stoichiometric air-fuel ratio stoich.

  As described above, according to the fourth control apparatus, when the predetermined condition (condition 1 and condition 2) is satisfied, in other words, when a large amount of NOx is predicted to flow into the catalyst 43, The target lean air-fuel ratio afLean is increased by the target lean air-fuel ratio correction amount ΔL compared to the case where the predetermined condition is not satisfied, and the target rich air-fuel ratio afRich is compared with the case where the predetermined condition is not satisfied. The target rich air-fuel ratio correction amount ΔR is decreased. As a result, the exhaust gas having a larger air-fuel ratio and the exhaust gas having a smaller air-fuel ratio alternately flow into the catalyst 43 as compared with the normal time (when the predetermined condition is not satisfied). However, since the target rich air-fuel ratio correction amount ΔR and the target lean air-fuel ratio correction amount ΔL are the same value, the “target rich air-fuel ratio afRich and the target when the predetermined condition (condition 1 and condition 2) is satisfied” are satisfied. The “average value of the lean air-fuel ratio afLean” becomes the stoichiometric air-fuel ratio stoich.

  As a result, the fluctuation range of the air-fuel ratio of the gas flowing into the catalyst 43 is increased, so that the oxidation-reduction reaction in the catalyst 43 becomes active, so that the amount of heat generated by the reaction is increased. Thereby, when the said predetermined condition is satisfied, the temperature of the catalyst 43 can be raised. Therefore, even after the engine 10 is accelerated and a large amount of NOx flows into the catalyst 43, the NOx reduction rate of the catalyst 43 is increased, so the catalyst 43 can purify much NOx. it can. As a result, the amount of unpurified NOx flowing out from the catalyst 43 can be reduced.

  As described above, the air-fuel ratio control apparatus according to each embodiment of the present invention includes an internal combustion engine including an air-fuel ratio control unit that controls the air-fuel ratio of the engine based on the output value Voxs of the downstream air-fuel ratio sensor 67. This is an air-fuel ratio control apparatus.

Further, the air-fuel ratio control means includes:
Condition determining means for determining whether or not a predetermined condition for predicting that an operation state in which a large amount of nitrogen oxide flows into the catalyst has arrived (steps 805 to 805 in FIG. 8, FIG. 11, FIG. 13, etc.) See step 830).
When the predetermined condition is satisfied, the air-fuel ratio of the engine 10 is controlled so that the concentration of the reducing agent in the catalyst 43 is increased as compared to the case where the predetermined condition is not satisfied (first to first). Third control device).

  Further, the first to third control devices are configured such that the average value of the air-fuel ratio of the engine 10 when the predetermined condition is satisfied is the average value of the air-fuel ratio of the engine 10 when the predetermined condition is not satisfied. By controlling the air-fuel ratio of the engine 10 so as to be smaller than the value, the concentration of the reducing agent in the catalyst 43 is increased when the predetermined condition is satisfied.

Alternatively, the air-fuel ratio control means includes
Condition determining means for determining whether or not a predetermined condition for predicting that an operating state in which a large amount of nitrogen oxide flows into the catalyst has arrived (see step 805 to step 830 in FIG. 14). Including
When the predetermined condition is satisfied, the air-fuel ratio of the engine 10 is controlled so that the temperature of the catalyst 43 rises compared to the case where the predetermined condition is not satisfied (fourth control device).

  As described above, the air-fuel ratio control means includes means for determining whether or not an operating state in which a large amount of nitrogen oxide flows into the catalyst 43 comes based on “whether the predetermined condition is satisfied”. .

  Therefore, when the engine 10 is accelerated and a large amount of NOx flows into the catalyst 43, each control device can set the NOx reduction rate of the catalyst 43 to a large value up to that point. More NOx can be purified. As a result, the amount of unpurified NOx flowing out from the catalyst 43 can be reduced.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, the first to fourth control devices can be combined with each other as long as no contradiction occurs. Further, the intake air amount Ga used in step 835, step 845, step 1130, step 1140, step 1330, step 1340, etc. may be the intake air amount correlation value described above.

Claims (10)

A catalyst disposed in an exhaust passage of the internal combustion engine;
A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
And air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel ratio Der Ru internal combustion engine of the mixture supplied to the prior SL engine based on the output value of the downstream air-fuel ratio sensor,
In an air-fuel ratio control apparatus for an internal combustion engine comprising:
The air-fuel ratio control means includes
A condition determination means for determining whether or not a predetermined condition for predicting that an operation state in which a large amount of nitrogen oxide flows into the catalyst has arrived ;
Based on the output value of the downstream air-fuel ratio sensor, a rich request for causing a gas having a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio to flow into the catalyst tends to become excessive as the oxygen storage amount of the catalyst becomes excessive. When the determination is made, the target of the air-fuel ratio of the internal combustion engine is set to a target rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and the oxygen storage amount of the catalyst tends to be insufficient, and the catalyst Target air-fuel ratio setting means for setting the target of the air-fuel ratio of the internal combustion engine to a target lean air-fuel ratio larger than the stoichiometric air-fuel ratio when it is determined that a lean request for inflowing air-fuel ratio gas has occurred;
Fuel supply amount control means for controlling the amount of fuel supplied to the internal combustion engine based on the set target air-fuel ratio;
Including
The target air-fuel ratio setting means further includes:
By setting the target rich air-fuel ratio, the smaller the air-fuel ratio than the target rich air-fuel ratio when the predetermined condition is not satisfied in the case where the predetermined condition is satisfied, before Symbol predetermined condition average of the air-fuel ratio of the internal combustion engine when but you satisfied, the air-fuel ratio of the internal combustion engine to be less than the mean value of the air-fuel ratio before SL internal combustion engine when the predetermined condition is not satisfied braking Gyoshi, the air-fuel ratio control apparatus configured so that increasing concentrations of the reducing agent in the catalyst as compared with the case where the said when a predetermined condition is satisfied the predetermined condition is not satisfied. The air-fuel ratio control apparatus according to claim 1,
The target air-fuel ratio setting means includes
When the change amount ΔVoxs per unit time of the output value of the downstream side air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | becomes larger than the lean determination threshold value dLeanth, the rich request is generated. And
When the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | becomes larger than the rich determination threshold value dRichth, it is determined that the lean request has occurred.
An air-fuel ratio control device configured as described above.   A catalyst disposed in an exhaust passage of the internal combustion engine;
  A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
  Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine that is the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output value of the downstream air-fuel ratio sensor;
  In an air-fuel ratio control apparatus for an internal combustion engine comprising:
  The air-fuel ratio control means includes
  A condition determination means for determining whether or not a predetermined condition for predicting that an operation state in which a large amount of nitrogen oxide flows into the catalyst has arrived;
  When the change amount ΔVoxs per unit time of the output value of the downstream side air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | is larger than the lean determination threshold value dLeanth, the state of the catalyst is oxygen. When it is determined that the catalyst is in an excess state, and the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | is greater than the rich determination threshold dRichth, the catalyst state is in an oxygen-deficient state. Catalyst state determination means for determining that
  The internal combustion engine when a lean delay time, which is a predetermined delay time including 0, has elapsed from the time when the catalyst state determining means determines that the state of the catalyst has changed from the oxygen deficient state to the oxygen excess state. When the target of the air-fuel ratio is set to a target rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and the catalyst state determining means determines that the state of the catalyst has changed from the oxygen excess state to the oxygen insufficient state Target air-fuel ratio setting means for setting the target of the air-fuel ratio of the internal combustion engine to a target lean air-fuel ratio larger than the theoretical air-fuel ratio when a rich delay time that is a predetermined delay time including 0 has elapsed from
  Fuel supply amount control means for controlling the amount of fuel supplied to the internal combustion engine based on the set target air-fuel ratio;
  Including
  The target air-fuel ratio setting means further includes:
  When the predetermined condition is satisfied by setting the rich delay time when the predetermined condition is satisfied to a time longer than the rich delay time when the predetermined condition is not satisfied Controlling the air-fuel ratio of the internal combustion engine so that the average value of the air-fuel ratio of the internal combustion engine is smaller than the average value of the air-fuel ratio of the internal combustion engine when the predetermined condition is not satisfied. An air-fuel ratio control device configured to increase the concentration of the reducing agent in the catalyst when the condition is satisfied as compared with the case where the predetermined condition is not satisfied.   A catalyst disposed in an exhaust passage of the internal combustion engine;
  A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
  Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine that is the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output value of the downstream air-fuel ratio sensor;
  In an air-fuel ratio control apparatus for an internal combustion engine comprising:
  The air-fuel ratio control means includes
  A condition determination means for determining whether or not a predetermined condition for predicting that an operation state in which a large amount of nitrogen oxide flows into the catalyst has arrived;
  When the change amount ΔVoxs per unit time of the output value of the downstream side air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | is larger than the lean determination threshold value dLeanth, the state of the catalyst is oxygen. When it is determined that the catalyst is in an excess state, and the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | is greater than the rich determination threshold dRichth, the catalyst state is in an oxygen-deficient state. Catalyst state determination means for determining that
  The air-fuel ratio of the internal combustion engine when a predetermined delay time has elapsed from the time when the catalyst state determining means determines that the state of the catalyst has changed from the oxygen deficient state to the oxygen excess state. The target air-fuel ratio is set to a target rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, and from the time when the catalyst state determining means determines that the state of the catalyst has changed from the oxygen excess state to the oxygen insufficient state. Target air-fuel ratio setting means for setting a target air-fuel ratio of the air-fuel ratio of the internal combustion engine to a target lean air-fuel ratio larger than the theoretical air-fuel ratio when a rich delay time including 0 that is a predetermined delay time has elapsed;
  Fuel supply amount control means for controlling the amount of fuel supplied to the internal combustion engine based on the set target air-fuel ratio;
  Including
  The target air-fuel ratio setting means further includes:
  When the predetermined condition is satisfied by setting the lean delay time when the predetermined condition is satisfied to a time shorter than the lean delay time when the predetermined condition is not satisfied Controlling the air-fuel ratio of the internal combustion engine so that the average value of the air-fuel ratio of the internal combustion engine is smaller than the average value of the air-fuel ratio of the internal combustion engine when the predetermined condition is not satisfied. An air-fuel ratio control device configured to increase the concentration of the reducing agent in the catalyst when the condition is satisfied as compared with the case where the predetermined condition is not satisfied.   A catalyst disposed in an exhaust passage of the internal combustion engine;
  A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
  Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine that is the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output value of the downstream air-fuel ratio sensor;
  In an air-fuel ratio control apparatus for an internal combustion engine comprising:
  The air-fuel ratio control means includes
  A condition determination means for determining whether or not a predetermined condition for predicting that an operation state in which a large amount of nitrogen oxide flows into the catalyst has arrived;
  When the change amount ΔVoxs per unit time of the output value of the downstream air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | becomes larger than the lean determination threshold value dLeanth, the air-fuel ratio of the internal combustion engine Is set to a target rich air-fuel ratio smaller than the theoretical air-fuel ratio,
  When the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | is larger than the rich determination threshold dRichth, the target air-fuel ratio of the internal combustion engine is set to a target lean value that is larger than the stoichiometric air-fuel ratio. Target air-fuel ratio setting means for setting the air-fuel ratio;
  Fuel supply amount control means for controlling the amount of fuel supplied to the internal combustion engine based on the set target air-fuel ratio;
  Including
  The target air-fuel ratio setting means further includes:
  By setting the rich determination threshold dRichth when the predetermined condition is satisfied to a value larger than the rich determination threshold dRichth when the predetermined condition is not satisfied, the predetermined condition is satisfied Controlling the air-fuel ratio of the internal combustion engine so that an average value of the air-fuel ratio of the internal combustion engine in the case where the predetermined condition is not satisfied is smaller than an average value of the air-fuel ratio of the internal combustion engine when the predetermined condition is not satisfied, An air-fuel ratio control apparatus configured to increase the concentration of the reducing agent in the catalyst when the predetermined condition is satisfied as compared with a case where the predetermined condition is not satisfied.   A catalyst disposed in an exhaust passage of the internal combustion engine;
  A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
  Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine that is the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output value of the downstream air-fuel ratio sensor;
  In an air-fuel ratio control apparatus for an internal combustion engine comprising:
  The air-fuel ratio control means includes
  A condition determination means for determining whether or not a predetermined condition for predicting that an operation state in which a large amount of nitrogen oxide flows into the catalyst has arrived;
  When the change amount ΔVoxs per unit time of the output value of the downstream air-fuel ratio sensor is a negative value and the magnitude | ΔVoxs | becomes larger than the lean determination threshold value dLeanth, the air-fuel ratio of the internal combustion engine Is set to a target rich air-fuel ratio smaller than the theoretical air-fuel ratio,
  When the change amount ΔVoxs is a positive value and the magnitude | ΔVoxs | is larger than the rich determination threshold dRichth, the target air-fuel ratio of the internal combustion engine is set to a target lean value that is larger than the stoichiometric air-fuel ratio. Target air-fuel ratio setting means for setting the air-fuel ratio;
  Fuel supply amount control means for controlling the amount of fuel supplied to the internal combustion engine based on the set target air-fuel ratio;
  Including
  The target air-fuel ratio setting means further includes:
  The predetermined condition is satisfied by setting the lean determination threshold value dLeanth when the predetermined condition is satisfied to a value smaller than the lean determination threshold value dLeanth when the predetermined condition is not satisfied. Controlling the air-fuel ratio of the internal combustion engine so that an average value of the air-fuel ratio of the internal combustion engine in the case where the predetermined condition is not satisfied is smaller than an average value of the air-fuel ratio of the internal combustion engine when the predetermined condition is not satisfied, An air-fuel ratio control apparatus configured to increase the concentration of the reducing agent in the catalyst when the predetermined condition is satisfied as compared with a case where the predetermined condition is not satisfied.   A catalyst disposed in an exhaust passage of the internal combustion engine;
  A downstream air-fuel ratio sensor disposed downstream of the catalyst in the exhaust passage;
  Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine that is the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output value of the downstream air-fuel ratio sensor;
  With
  The air-fuel ratio control means includes
  Including a condition determination means for determining whether or not a predetermined condition for predicting that an operation state in which a large amount of nitrogen oxide flows into the catalyst has arrived, and
  In the air-fuel ratio control apparatus for controlling the air-fuel ratio of the internal combustion engine so that the temperature of the catalyst rises when the predetermined condition is satisfied, compared to the case where the predetermined condition is not satisfied,
  The air-fuel ratio control means includes
  Based on the output value of the downstream air-fuel ratio sensor, a rich request for causing a gas having a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio to flow into the catalyst tends to become excessive as the oxygen storage amount of the catalyst becomes excessive. When the determination is made, the target of the air-fuel ratio of the internal combustion engine is set to a target rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and the oxygen storage amount of the catalyst tends to be insufficient and the catalyst has a leaner than the stoichiometric air-fuel ratio. Target air-fuel ratio setting means for setting the target of the air-fuel ratio of the internal combustion engine to a target lean air-fuel ratio larger than the stoichiometric air-fuel ratio when it is determined that a lean request for inflowing air-fuel ratio gas has occurred;
  Fuel supply amount control means for controlling the amount of fuel supplied to the internal combustion engine based on the set target air-fuel ratio;
  Including
  The target air-fuel ratio setting means further includes:
  The target rich air-fuel ratio when the predetermined condition is satisfied is set to an air-fuel ratio smaller than the target rich air-fuel ratio when the predetermined condition is not satisfied, and the predetermined condition is satisfied By setting the target lean air-fuel ratio when the predetermined condition is not satisfied to an air-fuel ratio larger than the target lean air-fuel ratio when the predetermined condition is not satisfied, the amount of heat generated in the catalyst is increased. An air-fuel ratio control device for increasing the temperature of the catalyst.   A three-way catalyst having an oxygen storage function disposed in the exhaust passage of the internal combustion engine;
  A downstream air-fuel ratio sensor disposed downstream of the three-way catalyst in the exhaust passage;
  Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine that is the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output value of the downstream air-fuel ratio sensor;
  In an air-fuel ratio control apparatus for an internal combustion engine comprising:
  The air-fuel ratio control means includes
  Condition determining means for determining whether or not a predetermined condition for predicting that an operating state in which a large amount of nitrogen oxide flows into the three-way catalyst comes;
  The air-fuel ratio of the internal combustion engine is determined based on the output value of the downstream air-fuel ratio sensor when it is determined that a rich request for flowing a gas having a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio into the three-way catalyst has occurred. It is determined that a lean request for causing a gas having a lean air-fuel ratio larger than the stoichiometric air-fuel ratio to flow into the three-way catalyst is generated based on the output value of the downstream air-fuel ratio sensor. When setting the air-fuel ratio of the internal combustion engine to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio,
  The average value of the air-fuel ratio of the internal combustion engine when the predetermined condition is satisfied during a period in which the rich request and the lean request are alternately generated is the rich request and the lean request alternately. The predetermined condition is satisfied by controlling the air-fuel ratio of the internal combustion engine so as to be smaller than the average value of the air-fuel ratio of the internal combustion engine when the predetermined condition is not satisfied in the generated period. And an air-fuel ratio control device configured to increase the concentration of the reducing agent in the three-way catalyst as compared to a case where the predetermined condition is not satisfied.   In the air-fuel ratio control device according to any one of claims 1 to 8,
  The predetermined condition is:
  The intake air amount correlation value, which increases as the intake air amount of the engine increases, is larger than a low air amount threshold value and smaller than a high air amount threshold value greater than the low air amount threshold value; and An air-fuel ratio control device that is a condition that is satisfied when at least one of the vehicle speed of the mounted vehicle is greater than the low-side speed threshold value and smaller than the high-side speed threshold value that is greater than the low-side speed threshold value. .   The air-fuel ratio control apparatus according to claim 9,
  The predetermined condition further includes:
  An air-fuel ratio control apparatus, which is a condition that is satisfied when a change amount per unit time of the intake air amount correlation value is smaller than a predetermined change amount threshold value.

Images